Method for producing nuclear fuel products with a high loading of LEU and corresponding nuclear fuel product

ABSTRACT

A method of producing a nuclear fuel product is provided. The method includes the steps of providing a core comprising aluminum and low-enriched uranium; and sealing said core in a cladding. The low-enriched uranium has a proportion of U235 below 20 wt %. The core includes more than 80 wt % of a mixture of UAl 3  phase and UAl 4  phase, and the mixture has a weight fraction of UAl 3  phase higher than or equal to 50%, or the core includes more than 50 wt % of UAl 2  phase. The core has a low-enriched uranium loading higher than 3.0 gU/cm 3 . The core includes less than 10 wt % in total of one or several material(s) taken from the list consisting of aluminum phase and aluminum compounds other than UAl 2  phase, than UAl 3  phase, and than UAl 4  phase. A corresponding nuclear fuel product is also provided.

The present invention relates to a method of producing a nuclear fuelcomprising low—enriched uranium and aluminium and to the nuclear fuelproduct obtained with said method.

BACKGROUND

Such a nuclear fuel product can be particularly used as a primary targetto produce elements such as molybdenum-99 (hereafter referred to as“Mo99”), which can in turn serve as a source of technetium-99 which is astandard beta emitter and therefore used for instance for equipmentcalibration, and in particular of metastable nuclear isomer oftechnetium-99 (Tc99m) used as radioactive tracer in nuclear medicine andbiology.

Such a nuclear fuel product can also be used as nuclear fuel forresearch nuclear reactors.

The nuclear fuel product generally takes the shape of a plate or acylinder with a core sealed by a cladding. It is intended to be put in anuclear reactor to be irradiated, in order to recover Mo99 as a fissionproduct of enriched uranium or to provide neutrons for researchapplications.

In the prior art, highly enriched uranium (hereafter referred to as“HEU”), that is to say with a content of U235 above 20 wt % and forinstance around 93 wt %, is generally used. Particles of UAl_(x) alloys,mostly containing UAl₃ and UAl₄ phases, are produced and mixed with analuminium powder. The mix is then pressed to produce a core comprisingUAl_(x) particles within an Al matrix, the UAl_(x) particlesrepresenting around 20-30% of the final core volume. The core is thenhot-rolled along with cladding plates to seal it. As a result, itslength is increased by a factor of about 400 to 600%, such plasticitycoming from its high aluminium powder content. In case of cylindricalshape, after hot-rolling the plate is bent and welded for instance byarc welding such as Gas Tungsten Arc Welding (GTAW) also known asTungsten Inert Gas (TIG) welding, by resistance welding . . . .

Due to growing concerns about potential misuse of HEU, there is a needfor switching from HEU to low-enriched uranium (referred to as “LEU”),that is to say with a U235 content below 20 wt %, usually around 19.75%.However, nuclear fuel product with LEU leads to less U235 content thanHEU nuclear fuel product and thus to a lower Mo99 recovery in primarytargets and lower neutron emission of nuclear fuel for research reactor.

For this reason, the particles of mostly UAl_(x), with x above or equalto 3, are replaced by particles mostly containing the UAl₂ phase, whichprovides a higher uranium-alloy density than both UAl₃ and UAl₄, hence ahigher U235 content to compensate the lower U235 enrichment of theuranium. The UAl₂ particles represent about 20-30% of the initial corevolume. The nuclear fuel product, after being rolled, undergoes athermal treatment in order to convert the UAl₂ phase into UAl_(x) in thecore, with x above or equal to 3 by using part of the Al matrix. TheUAl_(x) particles represent about 30-40% of the final core volume, theUAl₂, UAl₃ and UAl₄ phases amounting in total to about 50 wt % of thecore and the aluminium phase and the other aluminium compounds amountingto about 50 wt %. This thermal treatment generates huge geometricaldeformations leading to additional flattening steps with subsequentrisks of cladding failures or delamination.

The obtained uranium loading in the core ranges approximately from 2.7to 3.0 gU/cm³, 3.0 gU/cm³ being the technological limit achievable fornuclear fuel products made of UAl_(x) alloy, with the described priorart manufacturing processes.

SUMMARY OF THE INVENTION

An aim of the invention is to provide a method of producing a costeffective nuclear fuel product based on LEU which, when used as aprimary target, provides an improved Mo99 recovery and, when used as anuclear fuel for research reactor, provides a higher quantity ofneutrons.

To this end, the invention proposes a method of producing a nuclear fuelproduct, the method comprising the steps of:

-   -   providing a core comprising aluminium and low-enriched uranium;        and    -   sealing said core in a cladding;        wherein said core has a low-enriched uranium loading strictly        higher than 3.0 gU/cm³ and comprises less than 10 wt % of        aluminium phase and/or aluminium compounds other than UAl₂        phase, than UAl₃ phase, and than UAl₄ phase.

In other embodiments, the method comprises one or several of thefollowing features, taken in isolation or any technical feasiblecombination:

-   -   said cladding comprises one or several of an aluminium alloy, a        zirconium alloy such as Zircaloy-2, Zircaloy-4 or Zr—Nb alloy, a        Ni-based alloy such as Alloy 600, stainless steel such as AISI        304L or AISI 316L;    -   said cladding is an aluminium alloy comprising more than 95 wt %        of aluminium;    -   wherein said core comprises more than 80 wt % of a mixture of        UAl₃ phase and UAl₄ phase, said mixture having a weight fraction        of UAl₃ phase higher than or equal to 50%;    -   said core comprises more than 80 wt % of UAl₃ phase;    -   said core comprises more than 50 wt % of UAl₂ phase, preferably        more than 80 wt % of UAl₂ phase;    -   the step of providing said core comprises the substep of melting        low-enriched uranium and aluminium in a furnace to form a melt,        the proportion of low-enriched uranium in the melt being higher        than or equal to 68 wt % and lower than or equal to 82 wt %;    -   the proportion of low-enriched uranium in the melt is higher        than or equal to 71 wt % and lower than or equal to 75 wt %;    -   the proportion of low-enriched uranium in the melt is higher        than or equal to 73 wt % and lower than or equal to 75 wt %;    -   the proportion of low-enriched uranium in the melt is higher        than or equal to 75 wt % and lower than or equal to 82 wt %,        preferably higher than or equal to 78 wt % and lower than or        equal to 82 wt %;    -   the step of providing said core comprises the substeps of:        -   providing a ingot from the melt;        -   grinding said ingot to produce a powder;        -   compacting said powder to produce a compact; and        -   sintering said compact to obtain the core;    -   the step of providing said core comprises, prior to the substep        of compacting said powder, the substep of adding aluminium to        said powder, the weight proportion of aluminium in the powder        being lower than or equal to 10 wt %;    -   the step of sealing said core in said cladding comprises the        substeps of:        -   enclosing said core in framing elements to obtain a            sandwich; and        -   rolling said sandwich in order to extend a core length along            a rolling direction by a factor between 1% and 50%,            preferably between 5% and 30% and more preferably around            10%;    -   the step of providing said core comprises the substep of casting        the melt in order to make a compact;    -   said core also comprises an additional element, the weight        proportion of said additional element in the core being lower        than or equal to 3 wt %;    -   as an alternative to said substeps of melting LEU and aluminium        in a furnace, providing an ingot from said melt, and grinding        said ingot to obtain powder, said powder is obtained by an        atomization process, for example the atomization process        described in patent FR 2 777 688.

The invention also relates to a nuclear fuel product comprising:

-   -   a core comprising aluminium and low-enriched uranium; and    -   a cladding sealing the core;        wherein said core has a low-enriched uranium loading strictly        higher than 3.0 gU/cm³ and comprises less than 10 wt % of        aluminium and/or aluminium compounds other than UAl₂ phase, than        UAl₃ phase, and than UAl₄ phase.

In other embodiments, the nuclear fuel product comprises one or severalof the following features, taken in isolation or any technical feasiblecombination:

-   -   said cladding comprises one or several of an aluminium alloy, a        zirconium alloy such as Zircaloy-2, Zircaloy-4 or Zr—Nb alloy, a        Ni-based alloy such as Alloy 600, stainless steel such as AISI        304L or AISI 316L;    -   said cladding is an aluminium alloy comprising more than 95 wt %        of aluminium;    -   said core comprises more than 80 wt % of a mixture of UAl₃ phase        and UAl₄ phase, said mixture having a weight fraction of UAl₃        phase higher than or equal to 50%;    -   said core comprises more than 80 wt % of UAl₃ phase;    -   said core comprises more than 50 wt % of UAl₂ phase, preferably        more than 80 wt % of UAl₂ phase;    -   said core also comprises an additional element, the weight        proportion of said additional element in the core being lower        than or equal to 3 wt %.

The invention also relates to using the nuclear fuel product as anuclear fuel in a nuclear research reactor, for example in order toproduce neutrons.

The invention also relates to using the nuclear fuel product as aprimary target, for example to produce elements such as molybdenum-99.

BRIEF SUMMARY OF THE DRAWINGS

The invention and its advantages will be better understood on readingthe following description given solely by way of example and withreference to the appended drawings, in which:

FIG. 1 is a front view of a nuclear fuel product according to theinvention;

FIG. 2 is a cross section of the nuclear fuel product taken along lineII-II of FIG. 1;

FIGS. 3 and 4 illustrate the step of sealing the core of the nuclearfuel product shown in FIGS. 1 and 2.

DETAILED DESCRIPTION

FIG. 1 illustrates a nuclear fuel product 1 which is intended to be usedas a primary target in order to obtain Mo99 and, as such, to be put in anuclear reactor, or as a nuclear fuel for a research nuclear reactor inorder to obtain neutrons.

Typically, the nuclear fuel product 1 has the shape of a plate with alength of e.g. 180 mm for a primary target and until around 800 mm for anuclear fuel for research reactor, a width of e.g. 60 to 90 mm, and athickness of e.g. 2 mm. To obtain a cylindrical nuclear fuel product 1the plate is bent and welded on a diameter usually about 20 to 50 mm,e.g. 30 mm.

As illustrated by FIG. 2, the nuclear fuel product 1 comprises:

-   -   a core 3 comprising aluminium and LEU; and    -   a cladding 5 sealing said core 3.

By “LEU”, it is meant that the proportion of U235 in the uranium isbelow 20 wt %, for example around 19.75 wt %. The core 3 has a LEUloading strictly higher than 3.0 gU/cm³, preferably more than 4.0gU/cm³, and comprises, in addition to unavoidable impurities resultingfrom manufacturing processes, less than 10 wt % of Al phase and/oraluminium compounds other than UAl_(x) phase with x above or equal to 2.

Advantageously the core 3 comprises more than 90% of a mixture of UAl₂,UAl₃, and UAl₄ phases.

In specific embodiments, the nuclear fuel product 1 may be used as aprimary target or as a nuclear fuel, for example in a research reactorand the core 3 comprises more than 80 wt % of a mixture of the UAl₃ andUAl₄ phases, said mixture having a weight fraction of UAl₃ phase higherthan or equal to 50%, and preferably the core 3 comprises more than 80wt % of the UAl₃ phase.

In another specific embodiment, the nuclear fuel product 1 is dedicatedto primary targets and the core 3 comprises more than 50 wt % of UAl₂,preferably more than 80 wt % and even more than 90 wt % of UAl₂.

Advantageously, the core 3 also comprises an additional element, such assilicon, tantalum, niobium, or more generally any of the elementsdisclosed in patent FR 1 210 887, or a mixture thereof, the weightproportion of said additional element(s) in the core 3 being lower thanor equal to 3 wt % and preferably lower than or equal to 1 wt %.

The cladding 5 prevents the LEU from migrating from the core 3 tooutside the nuclear fuel product 1. It also holds the fission productsgenerated in the core 3 during its irradiation.

The material used for the cladding 5 may be any materials generally usedin nuclear reactor, i.e. an aluminium alloy, a zirconium alloy such asZircaloy-2, Zircaloy-4 or Zr—Nb alloy, a Ni-based alloy such as Alloy600, or stainless steel such as AISI 304L or AISI 316L.

Advantageously the material used for the cladding 5 is an aluminiumalloy comprising more than 95 wt % of aluminium.

For example the following alloys may be used:

-   -   EN AW-5754, also known as AG3, comprising about 3 wt % of        magnesium (ASTM B209/B308M),    -   EN AW-6061, comprising about 1 wt % of magnesium and 0.6 wt % of        silicon (ASTM B308/B308M), or    -   an AlFe1Ni1 alloy.

The method for producing the nuclear fuel product 1 generally comprisestwo main steps:

-   -   a first step of providing the core 3, and    -   a second step of sealing said core 3 in the protective cladding        5.

Examples of a method for producing the nuclear fuel product 1 will nowbe disclosed.

The core 3 is first produced through several substeps.

In a first substep, LEU and aluminium are melted in a furnace to obtainan U—Al_(x) for instance in an arc furnace, an induction furnace or aresistance furnace. Advantageously, the proportion of LEU in the melt ishigher than or equal to 68 wt % and lower or equal to 82 wt %,preferably higher than or equal to 71 wt % and lower than or equal to 75wt % and more preferably higher than or equal to 73 wt % and lower thanor equal to 75 wt %.

In an alternative, the proportion of LEU in the melt is higher than orequal to 75 wt % and lower or equal to 82 wt % and more preferablyhigher than or equal to 78 wt % and lower than or equal to 82 wt %.

If any, the above mentioned additional element(s) may be added to themelt in this first substep.

In a second substep, the melt is poured into a mould in order to form aningot.

In a third substep, the ingot is grinded in order to obtain a U—Al_(x)powder.

Advantageously the average size of the U—Al_(x) powder particles is lessthan 100 μm, for example around 40-70 μm.

For determining the aluminium powder particle size, laser granulometrycan advantageously be used, in accordance with standard NF ISO 13320.

The U—Al_(x) particles size is advantageously set using two sieves with40 μm and with 125 μm mesh. Using the sieves the U—Al_(x) powder isseparated into three fractions (below 40 μm, between 40 μm and 125 μm,and above 125 μm). The fraction above 125 μm is removed and thefractions between 0-40 μm and between 40-125 μm can be mixed in a givenproportion, for example 60 wt % of 0-40 μm and 40 wt % of 40-125 μm,leading to an average particle size of around 40-70 μm.

In a fourth substep, aluminium powder is added to the U—Al_(x) powder,the added aluminium being dispersed in the U—Al_(x) powder andrepresenting less than 10 wt % in the mixed powder.

If any and if not already added in substep 1, the above mentionedadditional element(s) may be added during this fourth substep.

In a fifth substep, the mixed powder is compacted to obtain a compact,for example having the shape of a parallelepiped. Advantageously, thecompact has approximately the final width of the core 3 in the nuclearfuel product 1, 80% to 90% of the final length of the core 3 and aroundtwice the final thickness of the core 3.

In a sixth substep, the compact is sintered, advantageously under vacuumat a temperature ranging between 500° C. and 1000° C., to obtain thecore 3, which has a porosity below or equal to 10%, preferably below 5%.Advantageously, the core 3 has a thickness comprised between 110% and120% of the thickness it will have in the nuclear fuel product 1.

The porosity of the compact is advantageously determined by weighing thecompact in air, then in water. During the latter measurement, thecompact is completely immersed in water, with no air bubbles present onthe suspension mechanism or on the compact. The porosity can then becalculated, knowing the theoretical density of the UAl_(x) material thatthe particles are made of.

As an alternative, to shorten treatment duration and/or reduce thequantity of residual porosities, the sintering substep can be performedunder high pressure, advantageously between 200 and 1000 bars, and at atemperature in the 400° C.-900° C. range.

As an alternative to the first, second and third substeps, the U—Al_(x)powder may be obtained by an atomization process, for example theatomization process described in patent FR 2 777 688.

As an alternative to the fifth and sixth substeps, the mixed powder maybe cold-sprayed on a surface, preferably a surface of the cladding 5,advantageously at a temperature between 300 and 500° C. Cold-sprayingresults in a dense and high quality deposit.

As an alternative no aluminium powder may be added in the fourthsubstep.

As an alternative to the second to sixth substeps, the melt may bedirectly cast in a mold having directly the size of the core 3, theadditional elements, if any, being added in the first substep.

The step of sealing the core 3 with the cladding 5 also comprisesseveral substeps.

In a first substep, as illustrated by FIG. 3, the core 3 is put in aframe 7, made of the same material as the cladding 5 or a materialallowing further sticking of the frame and the cladding, positionedalong the sides 10 of the core 3. It should be noted that, on FIGS. 3and 4, the width of the plates 9 and frame 7 have been exaggerated.

The frame 7 may comprise several pieces and preferably consists of onepiece.

In a second substep, the core 3 and the frame 7 are enclosed by an upperand a lower plates 9, the upper and the lower plates 9 forming thecladding, in order to form a sandwich 11 comprising the core 3, theframe 7, and the upper and lower plates 9. The upper and lower plates 9will form the cladding 5, once the sandwich 11 is sealed as disclosedhereunder.

The frame 7 and the upper and lower plates 9 are also referred to as“framing elements”.

The upper and lower plates 9 may be obtained by folding a sheet as shownon FIGS. 3 and 4. In FIG. 4, the sandwich 11 is in the process of beingclosed, by pressing on both external faces of the plates 9.

When using a folded sheet such the one shown on FIGS. 3 and 4, onlythree sides of the folded sheet must be bonded together in order to sealthe sandwich 11. When two separate plates are used, four sides must bebonded together to seal the sandwich 11.

In a third substep the sandwich 11 is hot-rolled to bond the frame 7 andthe upper and lower plates 9 together. The hot-rolling is preferablyperformed at a temperature higher than or equal to 300° C. andpreferably between 400-450° C., and preferably performed along adirection R.

The rolling rate, defined as the increase in length of the core 3 alongthe rolling direction R during the third substep, is advantageouslycomprised between 1% and 50%, preferably between 5% and 30% and morepreferably between 8-15%.

The third substep (hot-rolling in this example) brings the core 3 to itsfinal thickness and size and ensures a proper sealing of the core 3inside the cladding 5 formed by the frame 7 and the upper and lowerplates 9.

In a fourth substep, the final dimensions of the nuclear fuel product 1are adjusted by cutting its edges, by any cutting mean such as presscutting, water cutting, laser cutting . . . .

In a fifth substep, the nuclear fuel product 1 is submitted to achemical cleaning according to known processes.

Optionally cold-rollings at room temperature may be performed betweenthe third and fourth substeps to adjust the thickness and the length ofthe core 3.

If needed, an additional substep may be added after the fourth substepto adjust the thickness of the nuclear fuel product 1, for instance bymachining, chemical etching . . . .

As an alternative, in the second substep, an intermediate material, forinstance of Ni-alloy, may be positioned around the core 3 to avoidsticking of the core 3 on the cladding 5 during the third substep.

As an alternative to the third substep, the cladding 5 is welded on theframe 7 under vacuum, typically by electron beam welding, in order toseal the core 3 inside the cladding 5. To reduce the porosity of thecore 3 and the gaps between the components, the welded sandwich 11 isthen submitted to Hot Isostatic Pressing (HIP).

The relatively small rolling rate, advantageously between 1% and 50%,preferably between 5% and 30% and more preferably around 10%, makes therolling possible without cracking of the core 3, despite the relativelylow content, indeed the absence, of aluminium powder in the core 3. Therisk of an accumulation of the cladding material towards the ends of thecore 3 during rolling, known in the art as “dog-boning”, is reduced,leading to a possible reduction of the thickness of the cladding 5.

As a consequence of the reduced amount or the absence of aluminiumpowder in the core 3, the achievable technological limit for the uraniumloading in the core 3 is shifted from 3.0 gU/cm³ to strictly more than3.0 gU/cm³ for 80 wt % of a mixture of the UAl₃ and UAl₄ phases having aweight fraction of UAl₃ phase higher than or equal to 50% in the core 3.The technological limit is even shifted to more than 4.5 gU/cm³ withmore than 80 wt % of the UAl₃ phase in the core 3 and even above orequal to 6.0 gU/cm³ with more than 90 wt % of UAl₂ phase in the core 3,allowing to compensate for the decrease of uranium enrichment in U235isotope.

Thanks to the relatively high LEU loading in the core 3, the nuclearfuel product 1, provides an improved recovery of Mo99 when used as aprimary target, and a higher quantity of neutrons when used as a nuclearfuel in a nuclear research reactor.

Furthermore, the overall aluminium content of the nuclear fuel product 1being low, the amount of aluminium in effluents after dissolution of theirradiated nuclear fuel product 1 used as a primary target to recoverMo99 is moderate.

With an enhanced Mo99 recovery and less aluminium in the effluents, thenuclear fuel product 1 used as a primary target is very cost effective.

In case the nuclear fuel product 1 is used as nuclear fuel in a nuclearresearch reactor, the content of the UAl₂ phase in the core 3 being low,the risk of instability during irradiation is reduced.

Adding additional element(s) in the melt, such as silicon, tantalum,niobium . . . , the weight proportion of said additional element(s) inthe core 3 being lower than or equal to 3 wt %, allows reducing theweight proportion of the UAl₄ phase in the melt, compared to a meltwithout such additional element.

Adjusting the proportion of LEU in the melt at a level higher than orequal to 68 wt % and lower or equal to 82 wt % enables to obtain a core3 comprising at least 90 wt % of a mixture of UAl₂, UAl₃, and UAl₄,without any additional thermal treatment on the nuclear fuel product 1.

Adjusting the proportion of LEU in the melt at a level higher than orequal to 71 wt % and lower or equal to 75 wt % enables to obtain a core3 comprising at least 80 wt % of a mixture of UAl₃ and UAl₄.

Adjusting the proportion of LEU in the melt at a level higher than orequal to 73 wt % and lower or equal to 75 wt % enables to obtain a core3 comprising at least 80 wt % of UAl₃.

Using the nuclear fuel product 1 without UAl₂ phase avoids anymodifications of the existing manufacturing, irradiation and dissolutionprocesses and associated equipments and reactors.

Adjusting the proportion of LEU in the melt at a level higher than orequal to 78 wt % and lower or equal to 82 wt % enables to obtain a core3 comprising at least 80 wt % of UAl₂ without U metal phase.

Adding a small amount, less than 10 wt %, of aluminium powder in theU—Al_(x) powder obtained after grinding improves the plasticity of thecompact in view of further rolling.

Grinding the ingot into powder and then sintering the compact made fromthe powder provides a good homogeneity of the core 3 and allows reducingits porosity to a desired level. Setting the porosity level below 10%,preferably below 5%, helps increasing the LEU loading in the core 3.

Direct casting of the core 3 leads to a non-porous core 3 with a reducedAl content (no addition of Al powder) obtained by a simplifiedmanufacturing route.

HIP process allows working directly in the core geometry avoidingfailures of the nuclear fuel product 1 during rolling steps.

What is claimed is:
 1. A method of producing a nuclear fuel product, themethod comprising: providing a core comprising aluminium andlow-enriched uranium, the low-enriched uranium having a proportion ofU235 below 20 wt %; and sealing the core in a cladding; the corecomprising a first composition including more than 80 wt % of a mixtureof UAl₃ phase and UAl₄ phase, and the mixture having a weight fractionof UAl₃ phase higher than or equal to 50%, or the core comprising asecond composition including more than 50 wt % of UAl₂ phase, the corehaving a low-enriched uranium loading higher than 3.0 gU/cm³, the corecomprising less than 10 wt % in total of one or several material(s)taken from the list consisting of aluminium phase and aluminiumcompounds other than UAl₂ phase, than UAl₃ phase, and than UAl₄ phase.2. The method as recited in claim 1 wherein the cladding comprises oneor several of an aluminium alloy, a zirconium alloy, a Ni-based alloyand a stainless steel.
 3. The method as recited in claim 2 wherein thealuminium alloy comprises more than 95 wt % of aluminium, the zirconiumalloy is Zircaloy-2, Zircaloy-4 or a Zr—Nb alloy, the Ni-based alloy isAlloy 600 and the stainless steel is AISI 304L or AISI 316L.
 4. Themethod as recited in claim 1 wherein the core comprises the secondcomposition.
 5. The method as recited in claim 4 wherein the corecomprises more than 80 wt % of UAl₃ phase.
 6. The method as recited inclaim 1 wherein the core comprises the second composition preferablymore than 80 wt % of UAl₂ phase.
 7. The method as recited in claim 1wherein the step of providing the core comprises the substep of meltinglow-enriched uranium and aluminium in a furnace to form a melt, theproportion of low-enriched uranium in the melt being higher than orequal to 68 wt % and lower than or equal to 82 wt %.
 8. The method asrecited in claim 7 wherein the proportion of low-enriched uranium in themelt is higher than or equal to 71 wt % and lower than or equal to 75 wt%, wherein the core comprises the first composition.
 9. The method asrecited in claim 7 wherein the proportion of low-enriched uranium in themelt is higher than or equal to 73 wt % and lower than or equal to 75 wt%, wherein the core comprises more than 80 wt % of UAl₃ phase.
 10. Themethod as recited in claim 7 wherein the proportion of low-enricheduranium in the melt is higher than or equal to 75 wt % and lower than orequal to 82 wt % wherein the core comprises the second composition. 11.The method as recited in claim 7 wherein the step of providing the corecomprises the substeps of: providing a ingot from the melt; grinding theingot to produce a powder; compacting the powder to produce a compact;and sintering the compact to obtain the core.
 12. The method as recitedin claim 11 wherein the step of providing the core comprises: prior tothe substep of compacting the powder, the substep of adding aluminium tothe powder, the weight proportion of aluminium in the powder being lowerthan or equal to 10 wt %.
 13. The method as recited in claim 1 whereinthe step of sealing the core in the cladding comprises the substeps of:enclosing the core in framing elements to obtain a sandwich; and rollingthe sandwich in order to extend a core length along a rolling directionR by a factor between 1% and 50%.
 14. The method as recited in claim 10wherein the proportion of low-enriched uranium in the melt is higherthan or equal to 78 wt % and lower than or equal to 82 wt %.
 15. Themethod as recited in claim 10 wherein the core comprises more than 80 wt% of UAl₂ phase.
 16. The method as recited in claim 13 wherein therolling of the sandwich extends the core length by between 5% and 30%and more preferably around 10%.
 17. The method as recited in claim 6wherein the core comprises more than 80% of UAl₂ phase.
 18. A nuclearfuel product comprising: a core comprising aluminium and low-enricheduranium, the low-enriched uranium having a proportion of U235 below 20wt %; and a cladding sealing the core; the core comprising a firstcomposition including more than 80 wt % of a mixture of UAl₃ phase andUAl₄ phase, and the mixture having a weight fraction of UAl₃ phasehigher than or equal to 50%, or the core comprising a second compositionincluding more than 50 wt % of UAl₂ phase, the core having alow-enriched uranium loading higher than 3.0 gU/cm³ and comprises lessthan 10 wt % in total of one or several material(s) taken from the listconsisting of aluminium phase and aluminium compounds other than UAl₂phase, than UAl₃ phase, and than UAl₄ phase.
 19. The nuclear fuelproduct as recited in claim 18 wherein the cladding comprises one orseveral of an aluminium alloy, a zirconium alloy, a Ni-based alloy and astainless steel.
 20. The nuclear fuel product as recited in claim 19wherein the aluminium alloy comprises more than 95 wt % of aluminium,the zirconium alloy is Zircaloy-2, Zircaloy-4 or a Zr—Nb alloy, theNi-based alloy includes Alloy 600 and the stainless steel is AISI 304Lor AISI 316L.
 21. The nuclear fuel product as recited in claim 18wherein the core comprises the first composition.
 22. The nuclear fuelproduct as recited in claim 21 wherein the core comprises more than 80wt % of UAl₃ phase.
 23. The nuclear fuel product as recited in claim 18wherein the core comprises the second composition.
 24. The method asrecited in claim 16 wherein the rolling of the sandwich extends the corelength by around 10%.
 25. The nuclear fuel product as recited in claim23 wherein the core comprises more than 80 wt % of UAl₂ phase.